Silicon Bronze Screws

[Nhwhite]

Concerning Silicon Bronze screws; My Penobscot Trawler built in 1969 was refastened eleven years ago; Recently checking the garboard screws a good amount of detoriation was noted where the screw is exposed between the plank and the rib.Above the garboardd the screws were in better condition; I thought they were good for at least 20 years.Would appreciate comment. Nhwhite.

[Scott Rosen]

Sounds like electrolysis. Could be water in the bilge with dissimilar metals. Could also be stray current from your or some other boat nearby.

[Carlsboats]

Surveyors tell me that lots of bronze-fastened wooden boats (mine included, sadly) have disappearing screws. Your boat, dated 1969, is about the same age as my 1970 yawl, and I am advised by a just-completed survey to pop in a lot of new screws. Sometimes the screw thread disappears. Sometimes the wood around it is eaten away. Same difference: the old screws are barely
holding. A friend of mine recently rebuilt a Penbo and yes, he had to refasten her. You might check with other Penbo owners to get their experience, and ideas on how much rework is needed.

[Ken Hutchins]

Tell us more about these screws, this should not be happening. Where were the screws purchased? What kind of head? What was the country or origin? I hate to say it but I'm guessing the bad screws are from Asia and there are millions of them out there.

[cbob]

For what it's worth, refastened the underwater on an L-36, removed about 800 10 x 1 3/4 sil brz. Assume these were American made in the 50's. The replacements, # 12s came from Jamestown or Hamilton. Strip planked Phil. Mahogany on bent white oak. In the white oak no threads left on the removed screws and granulated scuz falling out of the hole, Those in the garboard rabbitt, the keel/backbone being Hond. Mahogany, were found to be sound, and most not replaced, after removing about fifty, (which were replaced with new, just for good practice) Attribute this this difference to the reaction within the chemical composition of the oak, rather than electrolys or substandard metalurgy. Could you have an oak keel, and of what wood are your frames/ribs? Would be interested, to confirm or dispute my theory/conclusion. cbob